1. Field of the Invention
The present invention relates to a non-monocrystalline silicon carbide semiconductor such as an amorphous silicon carbide semiconductor, (naturally including microcrystalline silicon carbide semiconductors), a polycrystalline silicon carbide semiconductor, and the like. The present invention also relates to a process for producing the semiconductor, and a semiconductor device employing the semiconductor.
2. Related Background Art
Silicon semiconductor films such as amorphous silicon semiconductor films and polycrystalline silicon semiconductor films are practically used for photoelectric transducing elements and semiconductor elements such as electrophotographic light-receiving members, solar cells, thin film transistors, and photosensors. In particular, solar cells are desired to to be improved further in the quality of the film in order to prevent photodegradation and to raise the transducing efficiency, and so forth.
Recently, amorphous silicon semiconductors used in usual solar cells, thin film transistors, and the like are reported to contain, in the amorphous silicon semiconductor film thereof, microvoids of 4 to 5 .ANG. in an average radius in a density of 2.times.10.sup.19 (cm.sup.-3).
Non-monocrystalline silicon carbide semiconductors are attracting attention for use as the material of a solar cell window. The non-monocrystalline silicon carbide semiconductors are also reported to have microvoids therein having an average radius of from 4 to 6 .ANG. in a density of not less than 5.times.10.sup.19 cm.sup.-3 (A. H. Mahan, D. L. Williamson, B. P. Nelson, and R. S. Crandall: "Characterization of microvoids in device quality, hydrogenated amorphous silicon by small-angle X-ray scattering and infrared measurements", Physical Review B, Vol. 40, No. 17, 15, Dec. 1989-1, 12024; and A. H. Mahan, B. P. Nelson, and D. L. Williamson: "Small angle X-ray scattering from microvoids in the a-SiC:H alloy", IEEE Transactions on Electron Devices, Vol. 36, No. 12, Dec. 1989, 2859)
The above-mentioned papers suggest that the microvoids relate to the state of the band end and the recombination centers, and further that hydrogen atoms are bonded in the microvoids, and the hydrogen atoms can migrate within the voids, which participates in photodegradation.
The inventors of the present invention have found that the microvoids in conventional non-monocrystalline silicon carbide semiconductors are in a shape of a circle or an ellipsoid having a depth of 2 to 5 atoms by observation with STM (scanning tunneling microscopy). Some stresses are assumed to be caused around the microvoids in consideration of arrangement of the atoms in the vicinity thereof. Thus, in conventional non-monocrystalline silicon carbide, a large number of carbon atoms and silicon atoms are considered to be displaced from the normal crystalline bonds.
Such displacement of the atoms of carbon and silicon disadvantageously prevents activation of doped impurities, and lowers the doping efficiency, and further causes trapping of the impurities in the microvoids to form bonding of the impurity in an inactive state. Further, presence of such microvoids and the distortion due to microvoids disadvantageously lowers the mobility of the charges.